A rotary drilling rig (or rotary drilling machine) is a type of piling equipment for coring. It mainly utilizes a power head to drive the drill rod, through which the power can be transferred to the drill tool (i.e., drill bit) for drilling. When the rotary drilling rig uses a friction-type drill rod, the power head of the rotary drilling rig relies on the two sides along the vertical direction of the drive key to realize forward and reverse rotation of the drill rod and transfer applied pressure. Therefore, after operating for some time the two sides along the vertical direction of the drive key can be worn down and become inclined. The side that drives the forward rotation of the drill rod is especially susceptible to wear and tear, and can be seriously abraded, causing the drive key of the power head of the rotary drilling rig to gradually lose its functions, thereby affecting the performance of the rotary drilling rig. When the rotary drilling rig uses machine lock drill rod, not only the two sides along the vertical direction of the drive key but also the pressure applying surface under the drive key can be worn down and become inclined. Thus, wear of the drive key is a common problem in rotary drilling rig equipment.
Currently, the drive key of the power head of the rotary drilling rig designed and produced by domestic as well as international manufacturers generally uses a three-piece drive key to realize driving and applying pressure to the drill rod. There are mainly two structural forms of the drive key: the welded and the detachable. The welded drive key cannot be replaced readily in the field when it is worn down. It has to be sent back to the manufacturer for reconditioning, thereby resulting in higher cost and longer service time.
The detachable drive key can be replaced in the field, however, there exist two problems when machine lock drill rod is used: 1) if a single drive key bears the applied pressure on its bottom, drive key bottom may be squeezed, warped, and deformed, the bolts of the drive key may be loosening, bending, or even breaking, thereby causing high failure rate; 2) if any of the two sides along the vertical direction of the drive key and the pressure applying side under the drive key has been worn down, the whole drive key unit has to be dissembled and replaced, thereby resulting in high replacing frequency and high cost. In addition, because of the restrictions of the structural space and the field conditions, it is very difficult to dissemble and assemble the drive key.